.PST export

It is astonishing to me that there still isn't a standard way to export an Outlook .pst into mbox or Maildir for import into other clients. It would be lossy, sure - you'd lose all kind of non-standard Microsoft "value-add". But that would be kind of the point: at its heart, a .pst is a minimally indexed zipfile of RFC-822 emails, with a scattering of MIME enclosures. All we want is to unmarshall those contents (and it's OUR mail). Why is this so hard?